Beam generating system for cathoderay tubes employing an ion trap



May 1958 w. BERTHOLD 2,836,752

BEAM GENERATING SYSTEM FOR CATHODE-RAY TUBES EMPLOYING AN ION TRAP Filed Feb. 9. 1954 INVENTOR vv. BERTHOLD Vz/jw TTORNEY United States Patent O BEAM GENERATING SYSTEM FGR CATHGDE- RAY TUBES EMPLOYING AN ION TBA? Wolfgang Berthold, Stuttgart-Wei] irn Dori, Germany,

assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application February 9, 1954, Serial No. 409,195

Claims priority, application Germany February 19, 1953 3 Claims. (Cl. 313-76) This invention relates to systems in generating electron beams for cathode ray tubes particularly of the type in which ions are trapped and prevented from impinging on the fluorescent screen.

in my corresponding U. S. application, Serial No. 390,328, filed November 5, 1953, there is described a beam generating system of the type in which an asymmetrical electron lens or diaphragm is arranged within the beam generating system, the asymmetrical lens distorting the field so that the electron beam is deflected away from the major axis of the tube. The electrons are deflected back by a conventional magnetic means while the ions are intercepted by a lens.

An object of the present invention is to improve the arrangement described in said application. The purpose of this improvemen is to produce a substantially larger angle of deflection of the electron beam away from the axis' This enables the use of a shorter-necked tube and is particularly advantageous with strong beam currents.

In accordance with a major feature of the present invention, the foregoing advantages are obtained by arching the asymmetrical lens within the beam generating system towards the cathode in accordance with a further improvement of the above arrangement, the lens which is arched towards the cathode is made elliptical or oval instead of circular. in this way it will be possible to change the shape of the focal point on the fluorescent screen.

The focal point or focusing spot may have either an oblong or a circular shape. By means of the ion trap magnet, whose deflecting field is generally insufiiciently homogeneous, an originally circular spot will be extended in the longitudinal direction (astigmatism). This distortion, or any other distortion which is caused by the system, can be compensated by the oval shape of the lens aperture, because generally a circular spot is to be preferred, since it has the smallest cross-section. However, if so required, also any other oblong shape of the focal point or focusing spot can be determined by the shape of the lens aperture, in which case the direction of the axis of the ellipse (oval) is decisive for the direction of the major axes of the oblong or longitudinal focusing spot.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood, by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a schematic diagram of a tetrode electron gun system,

Fig. 2 is a view of the apertures taken along the line A. .AofFig. 1,

"ice

Fig. 3 is a diagram illustrating the operation of the gun, and

Fig. 4 is a diagram showing the position of the ion trap magnet.

Referring now to the drawings, there is illustrated a cathode 1, a control electrode 2, a first lens electron 3 and an anode 4. The anode aperture 5 is arched towards the cathode. In Fig. 2 there is depicted the asymmetrical lens that is arched towards the cathode. In order to obtain an exact circular focusing spot on the fluorescent screen when employing a simple type ion trap magnet, the lens aperture is designed either oval or in the shape of an ellipse and the relation of the long semi-axis a to the short semi-axis b is approximately 1.15 to 1.0. The ion trap magnet is so arranged that the long semiaxis a points in the direction of the magnetic field lines of the ion trap magnet as shown in Fig. 1.

The electron beam 5e will be re-directed to the beam axis by means of the magnetic field 9. Fig. 3, of the commercial type ion trap magnet 10, Fig 4, consisting of a permanent magnet and two pole-shoes, while the ions 5i are further trapped by the aperture 11.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

l. A beam generating system for a cathode ray tube comprising a cathode electrode, a control electrode adjacent said cathode electrode, a first accelerating electrode adjacent said control electrode and an anode electrode, said control, accelerating, and anode electrodes being mounted serially along a given longitudinal axis and symmetrically disposed thereabout, said accelerating electrode and anode electrode each having an electron lens aperture through which the beam passes, one of said lenses being concentric with the longitudinal axis, the other of said lenses being eccentric with respect thereto, the lens of the anode electrode being arched towards the accelerating electrode, the aperture of the arched anode lens being elliptical.

2. A beam generating system according to claim 1 in which the long semi-axis of the ellipse of said elliptical aperture bears the ratio of 1.15:0.1 to l.

3. A beam generating system according to claim 2 further including a magnet for redirecting the deflected electrons while permitting the ions to be trapped, said long semi-axis of the ellipse pointing in the same direction as the magnetic field lines of said magnet.

References Cited in the file of this patent UNITED STATES PATENTS 2,472,766 Woodbridge June 7, 1949 2,515,305 Kelar July 18, 1950 2,562,242 Pohle July 31, 1951 2,565,533 Szegho et al Aug. 28, 1951 2,604,599 Breeden July 22, 1952 2,608,666 De Gier Aug. 26, 1952. 2,617,060 De Gier Nov. 4, 1952 2,637,828 Hoagland May 5, 1953 2,658,161 De Ano Nov. 3, 1953 2,673,305 Szegho Mar. 23, 1954 2,733,365 Hoagland Ian. 31, 1956 

